Expression of Two Members of the pMGA Gene Family of Mycoplasma gallisepticum Oscillates and Is Influenced by pMGA-Specific Antibodies

Abstract

Certain monoclonal antibodies and polyclonal antisera directed to pMGA, the major protein of Mycoplasma gallisepticum, were tested for the ability to influence the surface phenotype of the cell population which resulted from their inclusion in growth medium. The polyclonal antiserum and one monoclonal antibody (MAb 66) resulted in an alteration of surface phenotype; specifically, populations of cells grown either on plates or in broth cultures which contained these reagents ceased the expression of pMGA and instead expressed an antigenically unrelated new polypeptide (p82). Upon the removal of antibody, the progeny of these cells regained pMGA expression and produced antigenically sectored colonies. The basis of this switch between pMGA+ and pMGA− states was shown to be transcriptional. The p82 polypeptide, the expression of which resulted from growth of cells in antibodies, was another member of the pMGA gene family and was located just downstream from the pMGA gene normally expressed by the M. gallisepticum cells used. Collectively the results of this work suggest that this organism has evolved an unusual means of altering the antigenic composition of its surface in response to antibodies or to other environmental cues.

Sequence polymorphisms within the pMGA genes and pMGA antigenic variants in Mycoplasma gallisepticum

“…All pMGA genes with determined sequences (pMGA1.1p MGA1.9) have highly conserved leader peptide sequence and encode proline-rich regions (PRR) at the N-terminus with the cysteine (C 1 ) at the ¢rst position [6,8,10]. Our study was focused on the pMGA1.1 and pMGA1.2 genes because of the importance of their products as adhesins and immunodominant antigens [3,4,12].…”

“…Rabbit polyclonal antibodies pAb t pMGA against truncated recombinant pMGA1.1 (aa residues from 37 to about 300) and rabbit antiserum to pMGA1.9 were also used. Antibodies to pMGA1.9 protein do not react with pMGA1.1 or pMGA1.2 but only with pMGA1.9, which is a 82-kDa polypeptide synthesized in S6 strain [8,15].…”

“…The mAb 66 that reacts with pMGA1.1 and mAbs 71 and 86 that react also with pMGA1.2 were described elsewhere [4,8,15]. The mAb A3 reacts with pMGA1.1 and pMGA1.2 [14,16].…”

“…In M. gallisepticum, the pMGA gene sequences have been reported only for strains S6 and PG31 [11]. In addition, the N-terminal amino acid sequencing of the pMGA has been done for the F and R strains and con¢rmed a synthesis of proteins similar to the pMGA1.2 [8,9]. Data for other M. gallisepticum strains are not available.…”

“…We expected that the sequence data showing the di¡erences at the 5P-end of the pMGA gene might be useful for strain di¡erentiation. Patterns of pMGA expression and occurrence of antigenically distinct pMGA1.9 protein have been previously investigated only in a highly passaged S6 strain [8,15]. However, we already ¢fth passage [12].…”